import SwiftUI

struct TabItem: Identifiable, Hashable
{
    let id = UUID()
    let position: Int
    let color: Color
}

struct ContentView: View
{
    @State private var TabItems: [TabItem] =
    [
        TabItem(position: -1, color: .red),
        TabItem(position: 0, color: .green),
        TabItem(position: 1, color: .blue)
    ]

    @State private var selectedTab: Int = 0

    var body: some View
    {
        NavigationView
        {
            TabView(selection: $selectedTab)
            {
                ForEach(TabItems, id: \.position)
                { tab in
                    Rectangle()
                        .fill(tab.color)
                        .containerRelativeFrame([.horizontal, .vertical])
                        .overlay
                        {
                            VStack
                            {
                                Text("position \(tab.position)")
                            }
                        }
                        .tag(tab.position)
                }
            }
            .tabViewStyle(.page)
            .onAppear()
            {
                selectedTab = 0
            }
            .onChange(of: selectedTab)
            { _, new in
                if(new == TabItems.last!.position)
                {
                    print("swiped to end")
                    addTabFuture()
                }
                else if(new == TabItems.first!.position)
                {
                    print("swiped to beginning")
                    addTabPast()
                }
            }
            .navigationTitle("TabTest")
        }
    }

    func addTabFuture()
    {
        let tab = TabItem(position: TabItems.count, color: Color(red: .random(in: 0...1), green: .random(in: 0...1), blue: .random(in: 0...1)))

        TabItems.append(tab)
    }

    func addTabPast()
    {
        let tab = TabItem(position: TabItems.first!.position - 1, color: Color(red: .random(in: 0...1), green: .random(in: 0...1), blue: .random(in: 0...1)))

        TabItems.insert(tab, at: 0)

    }
}